Dialysis is a medical treatment that provides life-saving support to patients with insufficient renal function. The two principal dialysis methods are hemodialysis (HD) and peritoneal dialysis (PD). During HD, the patient's blood is passed through a dialyzer of a dialysis machine, while a dialysis solution (or, dialysate) is also passed through the dialyzer, generally in an opposite or countercurrent direction. A semi-permeable membrane within the dialyzer separates the blood from the dialysate and allows fluid exchanges to take place between the dialysate and the blood stream via diffusion, osmosis, and convective flow. These exchanges across the membrane result in the removal of waste products (e.g., such as solutes, like urea and creatinine) from the blood. These exchanges also help regulate the levels of other substances (e.g., sodium and water) in the blood. In this way, the dialyzer and dialysis machine act as an artificial kidney for cleansing the blood.
During PD, the patient's peritoneal cavity is periodically infused with dialysate. The membranous lining of the patient's peritoneum acts as a natural semi-permeable membrane that allows diffusion and osmosis exchanges to take place between the solution within the peritoneal cavity and the blood stream. Like HD, these exchanges across the patient's peritoneum result in the removal of waste products from the blood and help regulate the levels of other substances (e.g., sodium and water) in the blood.
Some dialysis systems also include a sorbent cartridge for regenerating (e.g., recycling) dialysate, substantially reducing the amount of dialysate needed to effect a complete treatment session. The sorbent cartridge can be designed to remove ammonium from the dialysate. However, the capacity of such cartridges to adsorb ammonium can diminish over time such that undesirable amounts of ammonium and ammonia may accumulate in the dialysate.